sudoku: constraints: add sudoku rules constraints

meson.build

@@ -9,6 +9,7 @@ project(
 )
 
 sources = [
+  'src/constraints.c',
   'src/main.c',
   'src/sudoku.c',
 ]

src/constraints.c

@@ -0,0 +1,50 @@
+#include "constraints.h"
+
+#include "sudoku.h"
+
+bool line_violation(const struct sudoku *grid, size_t i, size_t j) {
+    if (!grid)
+        return true;
+
+    for (size_t l = 0; l < 9; ++l) {
+        if (l == i)
+            continue;
+        if (grid->grid[l][j] == grid->grid[i][j])
+            return true;
+    }
+
+    return false;
+}
+
+bool column_violation(const struct sudoku *grid, size_t i, size_t j) {
+    if (!grid)
+        return true;
+
+    for (size_t c = 0; c < 9; ++c) {
+        if (c == j)
+            continue;
+        if (grid->grid[i][c] == grid->grid[i][j])
+            return true;
+    }
+
+    return false;
+}
+
+bool square_violation(const struct sudoku *grid, size_t i, size_t j) {
+    if (!grid)
+        return true;
+
+    const size_t x = i / 3;
+    const size_t y = j / 3;
+
+    for (size_t l = 3 * x; l < 3 * (x + 1); ++l) {
+        for (size_t c = 3 * y; c < 3 * (y + 1); ++c) {
+            if (l == i && c == j)
+                continue;
+            if (grid->grid[l][c] == grid->grid[i][j])
+                return true;
+        }
+    }
+
+    return false;
+}

src/constraints.h

@@ -0,0 +1,13 @@
+#ifndef CONSTRAINTS_H
+#define CONSTRAINTS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+struct sudoku;
+
+bool line_violation(const struct sudoku *grid, size_t i, size_t j);
+bool column_violation(const struct sudoku *grid, size_t i, size_t j);
+bool square_violation(const struct sudoku *grid, size_t i, size_t j);
+
+#endif /* !CONSTRAINTS_H */